In recent years, mobile broadband traffic has grown exponentially over the past years, thanks to the new generation of mobile terminals, such as smartphones, tablets and laptops. On the other hand, the consumers' demand and expectations of a consistent, high-quality and seamless mobile broadband experience are on the rise. Therefore, the capacity and the coverage of the current networks need to be improved to deliver high data throughput with very low latency to meet the consumers' expectations. Since spectrum has become a scarce resource nowadays, the deployment of heterogeneous networks, i.e., improving and densifying the existing macro cells (base stations) and complementing the macro cells with small cells, has been proposed to optimize the network performance.
FIG. 1 illustrates an example of a heterogeneous network. A heterogeneous network is composed of multiple radio access technologies, architectures, transmission solutions, and base stations of varying transmission power that can interoperate, thus creating a multilayer structure. Due to the different operating modes of the cells, and the unbalanced transmission power of the different base stations of the network, selecting the appropriate sever station can be challenging for the users equipments (UEs). Managing the interferences caused by the macro cell to the small cells and vice versa is one of the biggest challenges in the deployment of heterogeneous networks. Some Inter Cell Interference Coordination (ICIC) schemes, such as Enhanced Inter Cell Interference Coordination (eICIC) schemes, have been proposed to deal with this problem. These approaches can be divided into time domain techniques, such as almost blank subframes (ABS), and frequency domain techniques.
FIG. 2 illustrates an example of how a conventional interference control in the EICIC schemes is implemented. For example, in the eICIC schemes, a conventional interference control between a macro cell (e.g., eNB2) and a small cell (e.g., eNB1) is implemented by assigning a set of ABS (i.e., Subframes #4 and 5) to the macro cell, as illustrated in FIG. 2. The macro cell eNB2 will not transmit data in this set of ABS, such that the data transmission between the small cell eNB1 and the edge UEs can be done using this set of ABS, thereby mitigating interference from the macro cell to the edge UEs.
However, since the deployment of the small cells is usually irregularly and/or unevenly distributed, although the above conventional interference control may mitigate interference to the edge UEs served by the small cell from the other small cells in the heterogeneous network, the conventional schemes would waste precious time domain resources. For example, FIG. 3 illustrates the interference among the small cells eNB1, eNB2 and eNB3. As shown in FIG. 3, the small cell eNB1 serves the UE1, the small cell eNB2 serves the UE2 and UE3, and the small cell eNB3 serves the UE4 and UE5. Although the above-mentioned interference control assigning a uniform set of ABS (i.e., Subframes #4 and 5 as shown in the example of FIG. 3) to the eNB1 and eNB3 may mitigate interference to the UE2 and UE3 (served by eNB2) from the small cells eNB1 and eNB3, it would not use time domain resource efficiently. As shown in FIG. 3, although the small cell eNB2 may transmit data to UE2 and UE3 in Subframes #4 and 5, respectively, since the UE2 is not within the communication coverage range of the small cell eNB3, even if the small cell eNB2 transmits data to the UE2 during the ABS (i.e., Subframe #4), the collision will not occur. Therefore, the small cell eNB2 only needs to set Subframe #5 as ABS to eNB3. More precisely, the small cell eNB3 can transmit data on Subframe #4 so that time domain resource (i.e., Subframe #4) can be reused. Similarly, the small cell eNB2 only needs to set Subframe #4 as ABS to eNB1 as ABS to the small cell eNB1 so that Subframe #5 can be reused. In view of the above, it is clear that precious time domain resources will be wasted in the conventional schemes because unnecessary ABS may be assigned to the cells.